Carmichael’s Concise Review
of the subunits is β -actin; whereas the other subunits are Arp1, a protein related to actin. The presence of Arp1 and β -actin at an 8:1 ratio was confirmed by mass spectrometry- based quantitative proteomic analysis.
There are many other details of the study by Urnavicius et al. that lead to a novel hypothesis as to how the recruitment of dynactin by a cargo adaptor activates dynein. Previous studies with artificially dimerized dynein motor domains suggested that they self-associate in an auto-inhibited conformation unless they are separated. Urnavicius et al. suggested that dynactin activates the motor domains by reorienting two copies of the dynein heavy chain (DHC). Both DHC N termini are anchored parallel to each other, but the C termini are forced to twist apart because only one chain binds the second site on dynactin. This hypothesis explains why dynactin is built around an actin-like filament. The translational symmetry of the filament matches that of the DHC N termini, whereas the filament length provides additional binding sites that force dynein to adopt its active conformation. And that may be how a molecular motor works!
References [1] L Urnavicius et al ., Science 347 ( 2015 ) 1441 – 46 . [2] T e author gratefully acknowledges Dr. Andrew Carter for reviewing this article.
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2015 July
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